daybeers wrote: ↑Tue Jul 16, 2019 1:46 am
There still needs to be a citation for your math. Simple following spacing is not how traffic works.
Really? Golly, will California DOT suffice?
http://ccag.ca.gov/wp-content/uploads/2 ... ndix_B.pdf
Please read Table B1, take special interest with Line E, Row MSF(pcphpl) for freeways.
Note pcphpl equates to passenger cars per hour per lane.
Whether the speed is 70 mph, 65 mph, or 60 mph; the line reads 2,200 to 2,300 passenger cars per hour per lane as the lane's capacity. I suggest the same holds true for 55 mph, 50 mph, 45 mph, 40 mph, etc. although the table doesn't go that far - based upon the same principle I used earlier. Except California DOT isn't using one vehicle every two seconds, they are using one vehicle every 1.6 seconds.
Some more basic algebra; averaging 2200 and 2300, we should arrive at 2250.
2250 vehicles / hour x 1 hour/ 3600 seconds = 0.625 vehicles per second;
0.625/1 = 1/x ; 0.625x = 1; x = 1/0.625 = 1.6; or 1 vehicle per 1.6 seconds
In the Chart, the number of vehicles per hour remains the same indicating the lanes capacity, but the speed of the cars vary with congestion, and the density of cars per mile vary with the speeds.
Now go to page B-6 under Arterials, third paragraph. "Volumes on each roadway segment in each direction are divided by the capacity, estimated to be 1,100 vehicles per hour per lane. The capacity was estimated based on a saturation flow rate of 1,900 vehicles per lane and the assumption that El Camino Real would receive 60 percent of the green time."
They're using 1900 vehicles per hour per lane for El Camino Real. They reduced that to 1100 vehicles per hour per lane because the traffic lights are only green 60% of the time.
There you are, 1900 vehicles per hour per lane is standard California DOT saturation flow data point for multilane avenues and streets. It is not rocket science, all one needs is an understanding of basic junior high or middle school algebra and a little bit of common sense to come very close to what is real.
FYI, take another look at the Chart B1 again, the cars are almost maintaining posted speeds at 1800 vehicles per hour per lane. It's the additional 400 vehicles per hour that causes the 10 mph or so slower speeds on the freeway. So there is something to note of my vehicle every two seconds per lane safety statistic. Not only will you break and stop your vehicle in time before a crash, you also basically keep the freeway moving at the posted speeds.